There is emerging evidence that during development the neuropeptide oxytocin helps to organize neural circuits in the brain and that these organizational effects may help the brain develop the capacity to execute sex-specific and context-appropriate social behaviors later in life. This R15 proposes to use an animal model to better understand the role of oxytocin during fetal development. The working hypothesis of this grant is that fetal oxytocin is important to the development of the neural substrates that support sex-specific social behaviors in adulthood. To test this hypothesis two specific aims are proposed. The first aim will determine how the developing oxytocin system differs between female and males. The second aim will identify how developmental oxytocin differentially impacts female and male neurochemistry. The proposed research is significant because it would be the first to examine the function of oxytocin signaling during fetal development. Thus, it is expected that these experiments will reveal a novel role for oxytocin in organizing sex-specific brain circuits that are critical for typical displays of social behaviors. This knowledge is relevant to the mission of the NIH and to human health because across mammalian species oxytocin is important for social cognition and social functioning, and deficits in social behaviors are characteristic of several neurodevelopmental neuropsychiatric disorders. Thus, the experiments proposed are important because they will provide insight in the contributions of fetal oxytocin to the proper development of the male and female brain and ultimately to the expression of social behaviors.